RuntimeError on CI when running Tox on Windows, even if tests succeed

[marcofavoritobi]

Sometimes the tox command fails on CI when run on Windows, e.g. see https://github.com/bancaditalia/black-it/actions/runs/6051431578/job/16422861344:

=== 87 passed, 19 skipped, 1 deselected, 218 warnings in 188.28s (0:03:08) ====
Traceback (most recent call last):
.pkg: _exit> python C:\hostedtoolcache\windows\Python\3.10.11\x64\lib\site-packages\pyproject_api\_backend.py True poetry.core.masonry.api
  File "C:\hostedtoolcache\windows\Python\3.10.11\x64\lib\site-packages\tox\session\cmd\run\single.py", line 105, in run_command_set
    current_outcome = tox_env.execute(
RuntimeError: <_overlapped.Overlapped object at 0x00000168A4752F70> still has pending operation at deallocation, the process may crash
  py310: OK (350.94=setup[159.83]+cmd[191.11] seconds)
  congratulations :) (353.58 seconds)
Error: Process completed with exit code 1.

Probably it is an asyncio issue inside tox, as shown here for a similar error: https://stackoverflow.com/questions/69833208/runtimeerror-overlapped-overlapped-object-still-has-pending-operation-at-de.

Either fix the error, or do a workaround (e.g. check whether congratulations or py310: OK appears at the end of the output.